This invention relates generally to the field of papermakers felts and particularly to the formation of a pin seam in a papermakers felts.
Papermakers felt have conventionally been supplied to paper manufacturers as an endless belt. Such an endless belt is formed either by endless weaving of the base fabric prior to needling the felt batt into it, or by flat weaving a length of base fabric and then joining two ends of that fabric to form an endless belt prior to needling the batt. Recently, separable pin seams have become popular on such felts to simplify installation on the papermaking machinery. Such pin seamed felt include a plurality of interlocking loops formed at the opposite extremities of the fabric, with a pintle being inserted through the interengaged loops to form the fabric into an endless belt. Because such pin seams greatly simplify installation, they are rapidly becoming the standard seaming technique for papermakers felts.
While pin seamed felts have significantly simplified the installation of the felts on the presses and other machinery at the papermaking plant, they have brought certain inherent problems. Where the base fabric is of a single layer weave or of a very thin multiple layer weave, the pin seam frequently is thicker than the base fabric itself. When this occurs, passage of such a thickened seam over one of the press rollers or over the edge of an extended nip press tends to impart a bump or bounce to the press fabric and thus to the paper web being carried thereupon. This can result in unacceptably high levels of vibration in the operating presses.
To reduce the bounce caused by passage of the thickened pin seam over the press rolls or through the press nip, it is known to angle the seam as it passes over the rollers. Such angling conventionally has been accomplished by "cocking" the felt on the paper machine at the time it is installed. Also, where the felt is flat woven, it is known to weave or cut the fabric on a bias and then join the ends of the fabric on that bias to accomplish the angled seam. This is done either by weaving a rectangular piece of fabric and cutting the ends or sides at an angle, or by actually weaving the fabric as a parallelogram. All of these prior art practices are difficult to effect and have a high risk of nonuniformity in the finished fabric. Also, all of these procedures except cutting the ends of the fabric on a bias before sewing a seam result in a fabric in which the angled seam is not stable; that is, the seam attempts to straighten itself to extend perpendicular to the direction of travel of the felt. This occurs because the machine direction forces of tension encountered during operation on the paper machine will have a tendency to straighten the machine direction components in the fabric. This also causes the fabric to increase in length and to decrease in width.